Scientists with the National Oceanic and Atmospheric Administration on Friday photographed walrus packed onto a beach on a barrier island near Point Lay, an Inupiat Eskimo village 300 miles southwest of Barrow and 700 miles northwest of Anchorage.

The walrus have been coming to shore since mid-September. The large herd was spotted during NOAA's annual arctic marine mammal aerial survey, an effort conducted with the Bureau of Ocean Energy Management, the agency that conducts offshore lease sales.

An estimated 2,000 to 4,000 walrus were photographed at the site Sept. 12. The U.S. Fish and Wildlife Service, the agency that manages walrus, immediately took steps to prevent a stampede among the animals packed shoulder to shoulder on the rocky coastline. The agency works with villages to keep people and airplanes a safe distance from herds.

Young animals are especially vulnerable to stampedes triggered by a polar bear, a human hunter or a low-flying airplane. The carcasses of more than 130 mostly young walruses were counted after a stampede in September 2009 at Alaska's Icy Cape.

The gathering of walrus on shore is a phenomenon that has accompanied the loss of summer sea ice as the climate has warmed.

Pacific walrus spend winters in the Bering Sea. Females give birth on sea ice and use ice as a diving platform to reach snails, clams and worms on the shallow continental shelf.

As temperatures warm in summer, the edge of the sea ice recedes north. Females and their young ride the edge of the sea ice into the Chukchi Sea. However, in recent years, sea ice has receded north beyond continental shelf waters and into Arctic Ocean water 10,000 feet deep or more where walrus cannot dive to the bottom.

Walrus in large numbers were first spotted on the U.S. side of the Chukchi Sea in 2007. They returned in 2009, and in 2011, scientists estimated 30,000 walruses along one kilometer of beach near Point Lay.

Remnant ice kept walrus offshore in 2008 and again last year.

The goal of the marine mammals survey is to record the abundance of bowhead, gray, minke, fin and beluga whales plus other marine mammals in areas of potential oil and natural gas development, said NOAA Fisheries marine mammal scientist Megan Ferguson in an announcement.

"In addition to photographing the walrus haulout area, NOAA scientists documented more bowhead whales, including calves and feeding adults in the Beaufort Sea this summer compared to 2012," said Ferguson. "We are also seeing more gray whale calves in the Chukchi Sea than we have in recent years."

Environmental groups say the loss of sea ice due to climate warming is harming marine mammals and oil and gas development would add to their stress.

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